- Astove Island
Astove Island is part of the
Aldabra Group of theSeychelles . It is 38 kmSSE ofCosmoledo Atoll, located at (coord|10|06|S|47|45|E|). It is a raisedcoral island of most peculiar form: a single stretch of land, more than 1 km (nearly one mile) at the widest, almost entirely encloses a shallowlagoon . This has a maximum depth of 3 metres (10 ft), and the only exit is a winding passage in the southwest, called "Gueule Bras Channel".Astove Island measures nearly 6 km (3.7 miles) north to south and about 4 km (2.5 mi) at most east to west. The land area is 4.96 km²Verify source|date=April 2008 , and the total area including the
lagoon 9.5 km²Verify source|date=April 2008 . The only settlement, on the western coast, has been abandoned since the 1980s. There is a grassairstrip on the north east point of the island, and remnants of a formercoconut andsisal plantation . Today, the island is rarely visited - usually byscientists researching the lagoon'secology - but the near-vertical drop-off from its outerreef edge is a popular location fordiving cruises.Geology and geography
Astove's unusual structure has raised questions about its formation. It was suggested that Astove is not a true raised
atoll , but rather areef flat, with the lagoon being washed out later. In any case, the lagoon indeed grows slowly, owing to rainwater, acidic from thesoil 'shumic acid s, dissolving the lagoon'scarbonate rock bottom. This causes the unusual milky-white color of the lagoon's waters.Piggott (1961)]On the large land mass towards the western tip, exposed reef rock raises to some 5 m (15 ft) ASL. Elsewhere it is largely covered by
gravel ly debris. Dunes of up to 18 m (60 ft) line the windswept eastern rim of the island, and the eastern part of the lagoon is especially shallow due to the inblown dune sand. Astove Island'sfringing reef is just about 180 m (300 ft) wide. As noted above, beyond the reef's outer edge the seafloor drops down steeply, with a depth of 550 m (300fathom s) a mere 300 metres (900 ft) away from the shoreline.The
climate is dominated by the southeasttrade wind s which are most pronounced between April and November. Temperatures are around 28 °C (83°F) in the shade during that time, and slightly higher during the northwestmonsoon season. At that time,tropical cyclone s with torrential rain sometimes hit the island, but overall it is veryarid .Ecology
Flora
Astove Island has a very thin
soil layer overlying its rocky core, which is pockmarked with caverns.Guano of nestingseabird s has accumulated in these, and the western part has been worked over and some of the guano was mined in the past. Large stretches of the reef rock were stripped bare of vegetation, but some "Pisonia grandis " andWhite Milkwood ("Sideroxylon inerme ") persisted. The general vegetation on much of the island's western side isherbaceous plant s however, mainly the leadwort "Plumbago aphylla ", as well as "Stachytarpheta "species and thecrowfoot grass "Dactyloctenium pilosum ".Coconut Palm s ("Cocos nucifera") remaining from the struggling plantation along the western shore,Sisal ("Agave sisalana"), and wildcottonplant ("Gossypium") are also found here and there.Maize ("Zea mays") was planted by the guano miners, but presumably this plant which depends on constant care has disappeared since.The eastern dunes are overgrown with the
dropseed grass "Sporobolus virginicus " near the sea, and on the higher parts "bwa matlo " (Bay Cedar , "Suriana maritima ") shrubs are found. In more sheltered places, a regular scrubland of "vouloutye " ("Scaevola sericea ") andVelvet Soldierbush ("Tournefortia argentea"), with some "Pisonia", occurs. Here, the main herbs are fimbries ("Fimbristylis") and the parasiticvine "Cassytha filiformis ".The flats around the lagoon show a mixture of grassland (mainly
Pembagrass , "Stenotaphrum dimidiatum ") and "Pemphis acidula " scrub; in places, it is difficult to penetrate to the lagoon through the mass of "Pemphis" and "bwa matlo". Small Grey Mangroves ("Avicennia marina") line much of the southern half of the lagoon rim.Fauna
Astove Island is home to four landbirds:
* CosmoledoAbbott's Sunbird ("Cinnyris sovimanga buchenorum" or "C. abbotti buchenorum") - only occurs here and on nearbyCosmoledo
*Madagascar Cisticola ("Cisticola cherina")
*Pied Crow ("Corvus albus")
* CommonMadagascar White-eye ("Zosterops maderaspatanus maderaspatanus")There are few seabirds, probably due to the presence of
rat s andferal pig s, left behind when the settlement was abandoned. Unlike the other two atolls of the group, (Aldabra and Cosmoledo), there are nopredator -free islets except for a few small sandbanks close to the lagoon entrance. At the lagoon,Caspian Tern s ("Hydroprogne caspia") will often be seen but it is not known whether or not they ever breed on the sandbanks. IndopacificSooty Tern s ("Onychoprion fuscatus nubilosus") and WesternBlack-naped Tern s ("Sterna sumatrana mathewsi") have also been reported.Green Turtle s ("Chelonia mydas") remain very common here despite years of exploitation and remarkably high numbers will be seen on dives or from tender trips to the lagoon entrance close to high tide.Footnotes
References
* (1961): Notes on some of the Seychelles Islands, Indian Ocean. "Atoll Research Bulletin" 83: 1-10. [http://www.botany.hawaii.edu/faculty/duffy/ARB/076-84/83.pdf PDF fulltext]
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